Abstract

Effects of liveweight change during pregnancy and ewe shearing on lamb birth weight were studied using highly fecund Booroola-Merino cross Coopworth ewes. Following stratification on the basis of ewe live weight (mean 53.7 kg), age, breed, condition score, and previous (187) litter size, ewes were randomly allocated to a high (H) or low (L) early pregnancy (0.-49 days) nutritional treatment. Ewes on treatments L and H were offered sufficient feed to change their average live weight by 0 and 3 kg respectively between mating and 7 weeks post-mating. On the basis of litter size estimated by ultrasound scanning on day 50 of pregnancy, each of the 2 ewe groups was subdivided and allocated to one of 2 mid-pregnancy nutritional treatments (h and L) designed to change ewe body weight (live weight less conceptus weight) by 3 and 0 kg respectively in 7 weeks. One hundred and nineteen days after mating, half the ewes in each of the 4 nutritional subgroups were shorn and fed to the estimated metabolisable energy (ME) requirement of unshorn ewes. Lamb birth weights were recorded twice daily and within 12 hours of birth for 221 lambs born to 102 ewes conceiving at synchronised oestrus. High level of nutrition of ewes in early pregnancy increased birth weight of lambs by 46 (

JF, Smith, LT McGowan, JL Dobbie, and SH Smart

Proceedings of the New Zealand Society of Animal Production, Volume 49, , 249-254, 1989